BHP Billiton has increased full year iron ore guidance by 5 million tonnes, in a move that will surpass even the most optimistic expectations that were held by analysts.

The miner said today that production of its biggest money-spinner would now reach 217 million tonnes in the 2014 financial year rather than 212 million tonnes.

It is the second time this year that BHP has improved its iron ore production guidance and it came as full year coking coal guidance was also raised.

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BHP said the lift in iron ore expectations was enabled by a March quarter that saw a "relatively limited impact" from wet weather and cyclones.

That comment was a surprise after Rio Tinto's iron ore production from the same region was weaker than expected on the back of weather delays.

BHP produced 49.5 million tonnes of iron ore from the Pilbara in the March quarter, slightly better than analysts had expected.

The company enjoyed the benefits of a ramp-up in production from its Jimblebar mine, and its continued focus on incremental gains through efficiency and debottlenecking.

Baillieu Holst analyst Adrian Prendergast said the increased production guidance was a ''great result for a division that represents roughly half of company earnings''.

The iron ore price rose slightly overnight from $US117 per tonne to $US117.10 per tonne.

BHP's Queensland coking coal mines might be operating in a tough, low commodity price environment, but that hasn't prevented an increase in production guidance there either.

Guidance had previously been set at 41 million tonnes for the 2014 financial year, but that was a cautious target designed to allow for interruptions during the March quarter, when mines are often affected by wet weather and cyclones.

Having now come through that period largely unscathed, BHP's leadership felt comfortable increasing full year production guidance to 43.5 million tonnes.

The major negative from the quarterly results was a 2 per cent reduction in petroleum guidance on the back of weaker than expected production from BHP's US shale assets.

The Hawkville area in the Eagle Ford was specifically named for poorer than expected recoveries.

Full year guidance for copper was maintained at 1.7 million tonnes despite improved performance at Escondida in Chile.

Results were mixed across the division, and both Antamina and Olympic Dam will produce at below optimum levels in the remaining three months of the financial year.

But the miner announced that the official mineral resource at Escondida - which is already the world's biggest copper mine - has increased by 28 per cent on the back of brownfield drilling.

BHP considers its business to be built on four pillars; iron ore, coal, copper and petroleum, but the company is considering a possible fifth pillar in the shape of the Jansen potash mine in Canada.

But the miner demonstrated it was in no hurry to develop that fifth pillar, having proceeded much slower than expected on development of Jansen thus far.

BHP now expects to spend $US600 million on development of Jansen in the 2014 financial year, rather than the $US800 million that was originally forecast.

"We will continue to modulate the pace of development as we seek to time our entrance to meet market demand,'' the company said in a statement, adding that it expects the mine to properly ramp-up after 2020.

There was little further guidance from BHP with regard to the company's divestment campaign.

Fairfax Media reported earlier this month that a demerger of non-core assets was looming as the main option for BHP to divest of divisions like nickel, aluminium and possibly manganese among other assets.

BHP said further production capacity would be curtailed from its struggling aluminium division, particularly at Alumar in Brazil. The Bayside smelter in South Africa is also likely to close in the near future.

Mr Prendergast said there were few highlights from those non-core divisions in today's production report.

''BHP's alumina, aluminium, manganese ore and alloys, and nickel production were all down on the previous quarter in terms of production and mostly down year-on-year,'' he said.

BHP shares last traded at $37.78, and Mr Prendergast said the stock was "not expensive" at that price.

The release of March quarterly reports continues on Thursday with Evolution Mining and Sandfire Resources due to report.